And I just can't get it work, I have played with everything, but the triangle just won't appear, it always a green screen, so I'm thinking that somewhere something must be unique to OpenTK which is hindering me, that or I suck.

to pass the matrix directly. Both compile to the same code, so use whichever one you prefer.

The issue lies here:

MVP = Projection * View * Model

Change that to:

MVP = Model * View * Projection

and it will work.

A few years ago, OpenTK decided to match the XNA math library instead of something more typical to OpenGL. On one hand, this makes porting between XNA<->OpenTK easier. On the other hand, you need to flip the order of matrix multiplications compared to glm.